Minimum Fall For Flat Roof

The boards should be laid onto a vapour control layer and be covered with the waterproofing system.

Minimum fall for flat roof.

The recommended minimum fall for a flat roof is 1 80 0 72. However you can only use this pitch with built up roofing or specialized synthetic roofing. Cold roofs and warm roofs. I was thinking to also install a sheet of polycarbonate on the roof or even better perspex glass like window onto the sky.

My flat roof is 1 7 degrees. In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory. Proprietary preformed tapered insulation boards can provide drainage falls to a warm decked roof manufacturers recommend falls not less than 1 60. The minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run.

The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. This applies whether the waterproofing is a polymeric single ply membrane a reinforced bitumen membrane or another type listed in bs 6229 2018 the code of practice for flat roofs with continuously supported flexible waterproof coverings. This is the basis for calculating the angle which is approximately a 1 19 degree slope. It takes the manufacturer s recommendations the unique conditions of the roof as well as the skills and the expertise of the installer to arrive at the right slope.

Since they vary in quality as well as method of installation the choice preferred for a flat roof will ultimately have an effect on the final slope of the flat roof. There are two types of flat roof. I calculate that to be 0 7 degrees. According to bs 6229 bs 8217 flat roofs should be designed with minimum falls of 1 40 to ensure a finished fall of 1 80 can be achieved allowing for any inaccuracies in the construction.

As the single ply roofing association spra points out this type of flat roofing is strong durable completely sealed and usually lasts at least 25 30 years. Asphalt shingles continue to be the most widely installed roof covering option in north america. This applies to general roof areas along with any internal gutters. As opposed to old built up felt roofing with joins new single ply waterproof membranes are now most commonly used.